Devices; Poll Responses - HP 54501A Programming Reference Manual

Polling
HP-IB Devices.
Parallel Poll
is
the fastest
means
of gathering
device status when
several
devices
are connected to the
bus.
Each
device
(with
this capability)
can
be
programmed
to respond
with one bit of
status
when parallel polled. This
makes it possible to obtain the
status
of
several devices
in one operation.
If
a
device responds affirmatively to
a
parallel poll, more
information
about
its specific
status can
be obtained
by
conducting
a
serial
poll of
the
device.
Configuring Parallel
Poll Responses
Certain devices,
including
the
HP
54501A, can be remotely programmed
by
a
controller to respond
to
a
parallel poll.
A
device which is
currently
programmed for
a
parallel poll responds to the poll
by placing
its
current
status on one
of
the bus data
lines.
The response and
the data-bit number
can be
programmed by
the
PPC (Parallel
Poll Configure) statement.
Multiple
listeners cannot be
specified
in
this
statement.
If
more
than one
device
is to respond on
a
single bit, each device must be configured
with
a
separate
PPC
statement.
Example:
ASSIGN
©Device to
707
PPOLL CONFIGURE @Device;Mask
The
value
of Mask (any numeric expression can be
specified) is
first
rounded
and then used to configure the device's parallel response. The
least significant 3 bits
(bits 0 through
2)
of
the expression are
used to
determine
which data line the device
is to respond on (place its status
on).
Bit 3 specifies
the "true" state of the
parallel poll
response
bit of
the device.
A
value ofO implies that the
device's response
is 0
when
its
status
bit
message
is
true.
Example: The
following statement configures the device at address 07 on the
interface select
7
to respond
by placing
a
0
on
DI04
when
its
status
response
is
"true."
PPOLL CONFIGURE
707;4
Message Communication and System Functions
3-36
HP 54501A
Programming